According to the Driving Licence Regulations, you are allowed to drive the following on a category B licence:

Motor vehicles (except motorcycles and mopeds) with a maximum authorized mass not exceeding 3500 kg that are approved to carry a maximum of 8 passengers in addition the the driver.

Motor vehicles as stated in 1 towing a trailer with a maximum authorized mass not exceeding 750 kg.

Motor vehicles as stated in 1 towing a trailer with a maximum authorized mass exceeding 750 kg, as long as the combined (car and trailer) maximum authorized mass does not exceed 3500 kg.

Four-wheel motorcycles.Four-wheel motorcycles.

Mopeds.Mopeds.

From 2 it follows directly that you are allowed to drive a motor vehicle towing a trailer with a combined (car and trailer) maximum authorized mass of 4250 kg. From 2 it follows directly that you are allowed to drive a motor vehicle towing a trailer with a combined (car and trailer) maximum authorized mass of 4250 kg.